Electron bombarded semiconductor device

ABSTRACT

An electron bombarded semiconductor amplifier including an elongated envelope having an electron gun at one end to project an electron beam along said envelope, reverse biased semiconductor diodes forming a target at the other end of the envelope disposed to receive said beam and deflection means for deflecting the beam whereby more or less of the beam strikes the diodes forming the target.

imited States went 11 1 Bates et al.

ELECTRON BOMBARDIED SEMICONDUCTOR DEVICE Inventors: David J. Bates, LosAltos; Aris Silzars, Redwood C ity; Lester A. Roberts, Palo Alto; JamesA. Long, Los Altos, all of Calif.

Watkins-Johnson Company, Palo Alto, Calif.

Filed: Dec. 6, 1971 Appl. No.: 204,810

Assignee:

US. Cl 315/3, 315/3.5, 315/5.24, 313/65 AB, 330/43 Int. Cl. H0lj 23/16,HOlj 29/46, HOlj 29/70 Field of Search 315/1, 3, 5.24, 5.25, 3l5/3.5;313/65 AB, 66, 64.1; 330/43 References Cited UNITED STATES PATENTSKirkpatrick et a1 315/3 X 1 July 31, 1973 3,644,777 2 1972 Thomas et al.315/3 x 3,020,438 2 1962 Szikai 315 3 x 2,981,891 4 1961 116mm...v 315 3x 2,547,386 4 1951 Gray 315/3 x 3,504,222 3 1970 Fukushima..... 315 33,174,070 3 1965 Moulton 315/3 2,600,373 6/1952 Moore 315/3 PrimaryExaminerRudolph V. Rolinec Assistant E,tgminer axfie1d Chatmon, Jr.Attorney-- Paul D. Flehr, Aldo .1. Test et al.

[57] ABSTRACT An electron bombarded semiconductor amplifier including anelongated envelope having an electron gun at one end to project anelectron beam along said envelope, reverse biased semiconductor diodesforming a target at the other end of the envelope disposed to receivesaid beam and deflection means for deflecting the beam whereby more orless of the beam strikes the diodes forming the target.

7 Claims, 14 Drawing Figures PATENTED 3. 749 961 SHEET 2 BF 4 DAVID J.BATES LESTER A. ROBERTS ARIS SILZARS JAMES A. LONG I NVENTORS BY 2%,W m,F/G mumkfi W.

ATTORNEYS PATENIEDJULBI I915 3.749.961

SHEET 3 OF 4 77 76 ALUMINUM TOP CONTACT METAL OVERLAY 74 SILICON DIOXIDEDIFFUSED OR ION IMPLANTED P TYPE REGION DAVID J. BATES LESTER A. ROBERTSARIS SILZARS JAMES A. LONG v INVENTORS BY 9%,W, 72, ma, /W

' AT TORNE YS PATENIEDJUL31 I915 3.749.961

Q SHEEI b F 4 DAVID J. BATES LESTER A. ROBERTS ARIS SILZARS 3 JAMES A.LONG 62 58 INVENTORS BY F/G. wm wA/bw.

ATTORNEYS BACKGROUND OF THE INVENTION This invention relates toamplifiers and more particularly to an electron bombarded semiconductoramplifier.

Electron devices with semiconductor targets are known. However, suchdevices have been relatively low power, low frequency devices. Thedeflection means for the beam were primarily suitable for low frequencysignal inputs.

SUMMARY OF THE INVENTION AND OBJECTS It is a general object of thepresent invention to provide an electron bombarded semiconductor deviceincorporating improved laminar flow electron gun, beam deflection meansand an improved semiconductor target.

It is another object of the present invention to provide a highlyefficient, highly linear broad band electron bombarded amplifier.

The foregoing and other objects of the invention are achieved by anamplifier having an elongated envelope with a laminar flow electron gunprojecting a longitudinal electron beam disposed at one end of theenvelope, semiconductor diodes disposed at the other end of saidenvelope to form a target for said beam means, a delay line disposedbetween the gun and target in cooperative relationship with said beam todeflect the beam, and means for applying a signal to one end of thedelay line whereby it travels along the line in synchronism with theelectron beam to deflect the beam and control the amount of the beamwhich impinges upon the semiconductor diodes forming the target. Theinvention also incorporates an improved target configuration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view insection showing an electron beam semiconductor device in accordance withthe invention.

FIG. 2 is a plan view of the delay line beam deflection circuit.

FIG. 3 is an end elevational view of the delay line shown in FIG. 2,taken along line 3-3 of FIG. I.

- FIG. 4 is a front view showing the semiconductor target assembly ofthe present invention taken along the line 4-4 of FIG. 1.

FIG. 5 is a sectional view of the target assembly.

FIG. 6 shows a preferred semiconductor diode target.

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 1 showingthe mask disposed in front of the target.

FIG. 8 is a drawing of an RF lead-through for connecting to the diodetarget.

FIG. 9 is a schematic circuit diagram showing a single diode connectedin a Class A amplifier.

FIG. 10 shows the output voltage waveform at the load with lineardeflection of the beam for the circuit shown in FIG. 9.

FIG. 11 is a schematic circuit diagram showing two diodes connected in aClass B amplifier circuit.

FIG. 12 shows the output voltage waveform at the load with lineardeflection of the beam for the circuit shown in FIG. 11.

FIG. 13 shows a semiconductor diode target with integral bypasscapacitors.

2 FIG. 14 is a schematic circuit diagram of the device shown in FIG. 13.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. 1, a laminar flowsheet electron beam is formed by the electron gun 11. This beam isprojected along the tube envelope 12 through a deflection structure 13which imparts vertical motion to the electron beam due to the electricfields between its upper and lower conductors l4 and 16. This isfollowed by a drift space 117, beyond which is located the semiconductortarget assembly 13. The beam deflection at the targets is proportionalto the voltage applied to the input of the deflection structure. Reversebiased semiconductor diodes form the target. The target assembly anddiodes will be presently described.

When the diodes are bombarded by the incident electrons, hole-electronpairs are created within the reversed bias diode. The internal electricfields due to the reverse bias cause either holes or electrons, or both,of these carriers to flow through the diode and through the externalload Z FIGS. 9 and 11.

The incident velocity with which the beam electrons strike the target istypically chosen to be between 10 and 20 kV. For each electron enteringthe target, a current multiplication takes place which is approximately2,000:1 at I0 kV and 5,000:l at 20 kV. The current flow in the targetsis then proportional to the electron beam current striking the target.This basic property of the device leads to its linear amplificationproperties. A single diode target is suitable for use as a Class Aamplifier or as a dc. pulse amplifier. Twin targets such as shown inFIGS. 4, 5 and 13 are suitable for use as Class B RF or videoamplifiers. The manner in which the diode targets are connected to theload is shown in FIGS. 9 and 11 for Class A and Class B operation. AClass A device is a simple series connection of a dc. voltage source Vthe semiconductor diode 21 and the resistive load Z The load istypically a coaxial line or microstrip transmission line terminated inits characteristic impedance. The source voltage V,,,, divides itselfbetween a voltage drop across the diode V and a voltage drop across theload V In a Class A device, the electron beam is given a quiescentposition which illuminates one-half the diode. This gives a resultingquiescent current which is one-half of the peak current flowing during adeflection cycle.

The Class 8 device, FIG. 11, consists of two Class A circuits connectedto a common load Z The spacing between the two diodes in the target isarranged so that the quiescent position of the beam lies between the twotargets and, ideally, no current flows unless the beam is deflected.Deflecting the beam to the upper diode causes a current to flow so thatthe positive polarity of the voltage V is developed across the load.Deflecting the beam onto the other target causes the opposite polarityto be developed. Current flowing in the diode at any instant of time isdirectly proportional to the amount of beam incident on the diode. Thus,there is a linear relationship between the beam deflection and theoutput voltage V,, generated across the load. The ideal Class B devicehas the advantage that no current flows through the load when the beamis in its undeflected position. For purposes of simplicity, theremainder of the description will be directed to Class B type devices.

The electron gun 11 serves to develop a sheet beam which is directedalong the envelope towards the rectangular diode targets. The electrongun includes an indirectly heated strip cathode 26 for emittingelectrons, an apertured electrode 27 which serves as the grid and isclosely adjacent to the strip cathode 26. An anode is spaced from saidcathode electrode and cooperates therewith to provide a substantiallyuniform electric field at the surface of the cathode strip. Electronsemit normal to the entire cathode surface in a flat or sheet beam. Theanode also forms a divergent electrostatic lens along the path of thebeam. Accelerating and focusing means in the form of an electrode 29disposed further along the path of the beam accelerate and focus thebeam towards the semiconductor targets. The members 31 and 32 serve toprovide a field-free region for the beam to drift to the deflectionstructure 13. A suitable electron gun is described in copendingapplication, Ser. No. 149,445, filed June 3, 1971, entitled Laminar FlowElectron Gun and Method.

The upper plate 14 of the deflection system 13 is in the form of ameander line which defines a travelling wave deflection structure. Themeander line is in the form of a sheet or plate which includes slots a,15b extending inwardly alternately from opposite sides to form thestructure. This eliminates electron transit time, and high frequencydeflection limitations. It is a constant impedance, constant phasevelocity 50 ohm line disposed above the ground plane 16. It is drivenfrom a coaxial input connector 30 and the far end of the line is broughtout through another coaxial connector 35 to an external termination, orterminated internally. For maximum deflection sensitivity, the spacingbetween the meander line 14 and the lower ground plane 16 increases withdistance down the length of the tube. This prevents beam interception ofelectrons as the electron beam deflection increases toward the far endof the line. In the region where deflection is zero, at the input end ofthe line the spacing can be less which leads to increased deflectionsensitivity at the input end of the structure. Alternatively, forsomewhat reduced deflection sensitivity, the initial spacing isincreased and tapering of the spacing is not necessary. The line issubstantially wider than the electron beam with which it interactsthereby providing a more constant electric field to the beam. Theincreased width provides the desired impedance.

The meander line is supported by a pair of spaced rings 33 and 34carried in the tube envelope. The rings are each provided with a web 36,FIG. 3, through which extends a pair of spaced rods 37 and 38. Themeander line is disposed underneath the rods and is held or supported bythe rods by means of tabs 41 which are spot welded to the top of themeander line. The lower plate 16 is supported from the meander line bymeans of side strips 42 and 43, FIG. 3.

By way of example, the meander line design can be chosen to have a phasevelocity which is 0.2 times the velocity of light. This corresponds to asynchronous electron velocity of 10,000 volts. The velocity of the waveson the meander line structure is essentially independent of frequency.

The target assembly 18 is shown in FIGS. 4, 5, 6 and 7. The targetassembly includes a support 46 adapted to receive a sealing ring 47,FIG. 1, which is welded to the sealing ring 48 carried by the envelope.The support 46 receives a coaxial conductor 49 to be presently describedwith its inner conductor projecting into the tube envelope. The supportcarries a beryllium oxide substrate 51 on which the semiconductor diodesforming the target are mounted. Referring to FIG. 4, diodes 52 and 53are mounted on metallized areas 54 and 56, respectively. The metallizedarea 56 is connected by leads 57 to the center conductor of the coaxialinput and forms the common terminal. The metallized area 54 is connectedto a lead 58 which extends through the support and is sealed thereto as,for example, by means of a sealing ring 59 connected to the ceramicsleeve 60 which surrounds the lead. The other terminal of the diode 52is connected to the metallized area 56 forming the common connectionbetween the two diodes. The second terminal of the diode 53 is connectedto a metallized area 61 and thence to an input lead 62 which extendsthrough the support and is sealed as described above. The berylliumoxide substrate is metallized around the entire outer surface as shownat 63. This surface is connected to the outer conductor of the coaxiallead to maintain the area at ground potential. This also acts as theground return for the dc. supply. A mask 64, FIG. 7, is mounted on thefront wall of the mount 46 by means of screws 66. The mask is providedwith a pair of spaced windows 67 and 68 which expose only the activearea of the diodes 52 and 53 to the electron beam.

The diodes 52 and 53 may be formed by ion implantation on bulk materialor by diffusion into epitaxial material. Referring to FIG. 6, N-typesilicon 71 is bonded directly to a high thermal conductivity N+substrate 72. The upper surface includes a silicon dioxide layer 73which is provided with a window 74 through which is formed a P-typeregion 76. An aluminum metal overlay 77 provides the contact to theother terminal of the diode. The aluminum metal layer is sufficientlythin so that it can be penetrated by the electron beam to form thesecondary electrons within the bulk of the diode near the P-N junction.

The RF connection 49 may be of the type shown in FIG. 8 and include abody portion 81. A window sup port 82 placed in the upper bore of themember 81 extends upwardly to receive metallized window 83. The lowerportion of the window receives the pin assembly 84 which extendsupwardly to provide the coaxial interconnection and extends downwardlyconcentric with the metallic tube 86 and is maintained in spacedrelationship by a ring 87.

A target assembly 18 including bypass capacitors is shown in FIG. 13 andthe equivalent circuit is shown in FIG. 14. Since the target issubstantially the same as that shown in FIG. 4, the same referencenumerals are applied to like parts. The target assembly includes aberyllium oxide substrate 51 on which the semiconductor diodes fonningthe target are mounted. Referring to FIG. 13, diodes 52 and 53 aremounted on metallized areas 54 and 56, respectively. The metallized area56 is connected by leads 57 to the center conductor of the coaxial inputand forms the common terminal. The metallized area 54 is connected to alead 58 which extends through the support and is sealed thereto asdescribed above. The other terminal of the diode 52 is connected to themetallized area 56 forming the common connection between the two diodes.The second terminal of the diode 53 is connected to a metallized area 61and thence to an input lead 62 which extends through the support and issealed thereto. The beryllium oxide substrate includes a thirdmetallized area 91 connected to the outer conductor of the coaxial lead.This area extends under metal members 92 and 93 each of which forms oneplate of a capacitor and serves to form the other plate. A dielectric,not shown, is disposed between the plates. Leads 94 connect to the areas54 and 61. Referring to FIG. 14, the capacitors are shown at 96 and 97.The capacitors provide for higher frequency operation of the amplifier.

In conclusion, we have shown a new type of RF amplifier which exhibitslow pass amplifier characteristics and can operate from d.c. up to somepredetermined v cutoff frequency. In contrast to most microwave vacuumtube amplifiers, its dimensions do not grow inversely with frequency.Compact, light-weight amplifiers can be designed and built which havepower output capabilities up to several kilowatts. One of the mostsignificant characteristics of this device is its efficiency capability.The absence of the required magnetic focusing field greatly reduces theweight, size and complexity of the device.

We claim:

1. An electron bombarded semiconductor device comprising an evacuatedenvelope, an electron gun positioned at one end of said envelope toproject an electron beam along said envelope in a predetermined path,means comprising a delay line positioned along said beam to interactwith said beam, means for applying a signal to one end of said delayline whereby it travels along the line to interact with the beam todeflect the beam from the predetermined path responsive to a signalapplied to said line, a semiconductor target comprising a pair of spaceddiode devices each having first and second regions forming a p-njunction with one region adapted to receive said beam, with the beamimpinging between said devices when it is in said predetermined path andstriking said one region of one or the other of said devices whendeflected responsive to an input signal, means for interconnecting oneregion of said devices, a load having one terminal connected to saidinterconnecting means, and means for applying a voltage between theother terminal of said load and the other region of each of said devicesto reverse bias the semiconductor diode devices.

2. A device as in claim 1 including a mask disposed in front of saiddiodes whereby the beam strikes said diodes only when it is deflected.

3. A device as in claim 1 wherein said slow wave structure comprises ameander line spaced from a ground plane.

4. A device as in claim 3 wherein said meander line comprises a platehaving slots extending inwardly alternately from opposite sides.

5. A device as in claim 4 including a ground plane spaced from saidplate with the spacing increasing in the direction of the target.

6. A device as in claim 1 including a non-conductive support, conductivepads formed on said support to receive said diode devices and form aconnection with one terminal of each device, a conductive film spacedfrom said pads and forming a ground adapted to be connected to the otherterminal of said load, a coaxial conductor having its outer conductorconnected to said ground and its inner conductor to a terminal of eachof said diode devices to form the interconnection and adapted to beconnected to said one terminal of said load and means providingelectrical connection to each of the other terminals of said diodedevices for applying said voltage.

7. A device as in claim 6 including capacitors carried by said supportand connected between the conductive film forming ground and the meansproviding electrical connection to the other terminals.

1. A n electron bombarded semiconductor device comprising an evacuatedenvelope, an electron gun positioned at one end of said envelope toproject an electron beam along said envelope in a predetermined path,means comprising a delay line positioned along said beam to interactwith said beam, means for applying a signal to one end of said delayline whereby it travels along the line to interact with the beam todeflect the beam from the predetermined path responsive to a signalapplied to said line, a semiconductor target comprising a pair of spaceddiode devices each having first and second regions forming a p-njunction with one region adapted to receive said beam, with the beamimpinging between said devices when it is in said predetermined path andstriking said one region of one or the other of said devices whendeflected responsive to an input signal, means for interconnecting oneregion of said devices, a load having one terminal connected to saidinterconnecting means, and means for applying a voltage between theother terminal of said load and the other region of each of said devicesto reverse bias the semiconductor diode devices.
 2. A device as in claim1 including a mask disposed in front of said diodes whereby the beamstrikes said diodes only when it is deflected.
 3. A device as in claim 1wherein said slow wave structure comprises a meander line spaced from aground plane.
 4. A device as in claim 3 wherein said meander linecomprises a plate having slots extending inwardly alternately fromopposite sides.
 5. A device as in claim 4 including a ground planespaced from said plate with the spacing increasing in the direction ofthe target.
 6. A device as in claim 1 including a non-conductivesupport, conductive pads formed on said support to receive said diodedevices and form a connection with one terminal of each device, aconductive film spaced from said pads and forming a ground adapted to beconnected to the other terminal of said load, a coaxial conductor havingits outer conductor connected to said ground and its inner conductor toa terminal of each of said diode devices to form the interconnection andadapted to be connected to said one terminal of said load and meansproviding electrical connection to each of the other terminals of saiddiode devices for applying said voltage.
 7. A device as in claim 6including capacitors carried by said support and connected between theconductive film forming ground and the means providing electricalconnection to the other terminals.